Electronic tube



Jan. 18, 1955 w. c. MILLIGAN 2,700,122

ELECTRONIC TUBE Filed Jan. 21. 1950 bygZ/MM M575 United States Patent O ELECTRONIC TUBE William C. Milligan, San Antonio, Tex.

Application January 21, 1950, Serial No. 139,907

Claims. (Cl. 315-342) This invention relates to a gaseous discharge device, and more particularly to a gaseous discharge device provided with means for continuously controlling thev ow of space current therein.

For many years there have been two principal types of electron discharge devices, namely, the high vacuum tube and the gas-filled tube. The outstanding advantage of the high vacuum tube lies in the fact that continuous control of the ow of space current may be had by means of a suitable control grid. The disadvantage of the high vacuum tube is its relatively high effective resistance between the cathode and 'the' anode and its resultant inefficient operation. The outstanding advantage of the gas-filled tube has been its high efficiency, but this has been offset by its lack of continuous control over the flow of space current.

More recently, efforts have been made to eiciently control the space currents of gas-filled tubes, and there resulted what is known as a cathanode-type of tube construction. This cathanode-type of tube construction provides a compromise between the eiiciency of a gaslled tube and the control possible in a vacuum tube.

The term cathanode itself has been used to designate a blocking anode which is an electrode in the form of a plate or equivalent structure having very small openings therethrough.

In order to understand the presentinvention, it is irnportant to note certain marked differences between this so-called cathanode-type of tube construction and the tube of the present invention. The cathanode-type of tube construction requires a relatively high plate or anode potential because of the high drop between the cathanode and the plate. The cathanode-type of tube, in the region between the cathanode and the plate, acts in a manner similar to a vacuum tube. Another apparent characteristic Aof the cathanode-type of tube construction lies in the high current drawn by the cathanode with respect to that drawn by the plate.

In the tube of the present invention, as will presently be described, a relatively low plate voltage'may be used, and no blocking anode is used. In the .cathanode type of tube construction, a control grid is located in the region which is free of ionization which lies between the cathanode and the plate. While this allows a sensitive control of space current, it does not permit eicient operation of the tube.

It is, of course, well recognized that the eiect of the grid has practically no effect upon the anode current in a gas-filled tube When it is negative which isV due to the space-charge sheath of positive ions that forms around the negative grid. When conduction starts, a positive ion sheath forms around the cathode and the remaining space between the anode and the cathode becomes filled with a plasma in which the concentrations of positive ions and electrons are approximately equal and in which the potential is constant and practically equal to that of the anode.

When the grid is made negative with respect to the space, it repels electrons and attracts positive ionsv so that the space adjacent to it is filled with positive ions all moving toward the grid under lthe influence of the electric field. When an equilibrium rate of flow of positive ions is reached, the total positive charge in the space outside the grid wire equals the negative charge induced on the grid wire by the applied voltage. Under these conditions, the net charge insidethe boundary of the positive ion sheath is zero, and the plasma/outsidel the sheath is unaffected by the presence of the negative grid. Consequently, conduction between the anode and the cathode can take place through the remaining plasma between the grid sheaths, and the negative grid does not control or stop the anode current.

One effort in the past to control the ilow of anode current in a gas-filled tube has been to make the spacing between adjacent grid elements so small that the positive ion sheaths associated with each portion may be made to overlap.

The present invention makes use of neither a cathanode element nor a ne mesh grid. Instead, a control grid having widely open spacings of the type commonly employed in vacuum tubes is used, in combination with a magnetic field. This magnetic lield coacts with the electric field to render the region between the plate and cathode stratified into layers of high and low ionization intensity. The result of this stratification of the plasma region tends to prevent the formation of an ion sheath around the grid that would otherwise neutralize the grid. This has been found in practice to give the tube the desired continuous control of space current, while at the same time avoiding the losses inherent in the cathanodetype of construction or in the ne mesh grid type of construction. Thus, the present invention enables full advantage to be taken of the high eliiciency possible in a gas-lilled tube and yet, at the same time, obtain the continuous control which is possible in a vacuum tube.

An object of the present invention is to provide a gas-filled tube having its space .current eiiciently and continuously regulated by a control grid and a cooperating magnetic eld.

Another object of the present invention is to provide a gaseous discharge tube having effective grid control of space current with the aid of a magnetic field substantially aligned with the electric iield formed between the tube elements.

A further object of the present invention is to provide a novel current control means for gas-filled tubes by providing means to stratify the plasma into regions of high and low ionization intensity.

A still further object of the present invention is to provide a novel method and means for reducing random motion in the space current and to reduce the tendencyl for electrons to recombine with positive ions in the tube.

Another and further obpect of the present invention is to provide a novel method and means for substantially preventing the formation of a positive ion sheath around the control grid of a gaseous discharge tube.

Still another and further object of the present invention is to provide a novel gas-filled tube effective for operation at high frequencies.

Another and still further object of the present invention is to provide a novel multi-element gas-filled tube.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization, manner of construction, and method of operation, together with further objects and advantages thereof lmay best be understood by reference to the following description taken in connection with the accompanying drawing, in which:

Figure l is a vertical sectional view of one embodiment of the present invention;

Figure 2 is a horizontal sectional view ofthe embodiment of the invention shown in Figure l as taken along the line II-II of Figure 1;

Figure 3 is a vertical sectional view of a second embodiment of the present invention having a second grid electrode and having the tube elements, the space current liow, and the magnetic eld all aligned axially with the tube; and

Figure 4 is a vertical sectional view of a third embodiment of the present invention with the elements arranged for push-pull action and in avform usually described as a Patented Jan. 18, 1955 glass or similar material is filled with a suitable gas such as mercury in a quantity sutiicient to support a gaseous discharge. This tube 11 encloses an indirectly heated cathode 12 and a double-faced planar anode 13. Closely surrounding the entire anode 13 is al wire control grid 14 which is wound with spacings that are large compared with the wire diameter. On a line bisecting the cathode 12 and the anode 13, two magnetic pole faces 15 of opposite polarity are aligned. I t will, of course, be understood that one of the poles 15 is a north pole and the other pole 15 is a south pole as indicated in the drawing. These magnetic poles 15 are positioned outside of the tube 11 and arranged to establish a magnetic field within the tube in a direction substantially parallel to the direction of flow of space current from the cathode 12 to the anode 13.

When suitable potentials are supplied to the cathode 12 and the anode 13, the latter being positive with respect to the former, an electric field is established which is substantially in alignment with the magnetic field. A subsequent application to the control grid 14 of a potential which is considerably less than the potential applied to `the anode 13 in combination with the aforesaid magnetic and electric fields stratifies the ionized region within the tube which is occupied by the plasma. To indicate the stratification of the plasma within the tube, I have shown in Figure l of the drawing alternate regions 16 and 17 which have been observed in practice to be regions ofglow and regions of dark, respectively. The regions 16 of glow have the characteristic glow which is well known in a typical gaseous discharge device during times when ionization is taking place. The alternate spaces 17 are dark but are believed by me to be regions of ionization of different intensity from the stratified regions 16 where the glow takes place.

lt is important to understand that the above described physical structure has been operated with extreme success and efficiency. A complete explanation of the theory underlining the reasons why the tube operates as an extremely efiicient device with the complete control of a high vacuum tube but with the high eliciency of a gas tube is not fully understood. One explanation of the underlying phenomenon, however, will be hereafter set forth.

When the cathode heater leads 18 are energized, the cathode 12 which is coated with an electron emitting material 19, such as an alkali earth metallic oxide, gives off an abundant electron space current.

The electrons accelerated in the electric field ionize the gas by collision. is due to those electrons which have been accelerated to such a point that where they strike a gas molecule with sufficient speed, one of the electrons moving in an orbit in the molecule is driven to an outer orbit or is freed. This bombardment of the gas molecules by the high speed electrons being emitted by the cathode results in the formation of positive ions. The process by which an electron is completely separated from an atom is known as ionization. The part of the atom that remains after ionization is called a positive ion. After ionization has occurred, both the electron and the positive ion are free to move independently, and if they are in an electric field, they are accelerated and acquire kinetic energy. They are also inliuenced by magnetic elds. It is to be emphasized, however, that the ion possesses ionization energy as well as its kinetic energy and will release the former whenever any electron recombines with it to form a normal atom. It is the recombination of the electron with the positive ion that creates the characteristic glow normally associated with gas tubes.

One of the more important effects of ionization in gases is the neutralization of the electronic space charge. Because of their relatively large mass, and consequently low speed for a given energy, positive ions remain much longer in the space between the electrodes than do the electrons. They, therefore, for a given current, are much more elec tive in producing space charge.

ln connection with the present explanation, it is, of course, important to bear in mind that the inner electrode space may be divided generally into two regions of very different characteristics. The first region is the cathode clark space which is the result of a positive ion sheath surrounding the cathode. The second region is the plasma. This plasma region is a region of small voltage gradient because of the presence of electrons and This ionization of the gas by collision agotarse.

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positive ions in amounts that produce a small net space charge. The electrons are` projected into the plasma from the cathode, and because of the frequent collisions with the gas molecules acquire a random distribution of velocities. A few of these collisions produce ions and new electrons which help to maintain the plasma. In addition, the electrons acquire a drift velocity toward the anode because of the small electric field along the plasma.

In the tube of the present invention, it is important to bear in mind that while there is a dark space adjacent the cathode, as well as stratified dark spaces between the cathode and the control grid, these two dark spaces are not similar- The dark spaces 17 are regions of ionization as are alsothe glow regions 16, the difference between the two being that the dark regions 17 do not have any substantial amount of recombination of electrons with positive ions taking place.

To confine the ionization to a controlled region without requiring excess magnetic liux and to prevent the ac` cumulation of charge onl the inner walls of the tube 11, a cylindrical conducting shield 21 is provided together with mica disks 22 across both ends of the shield 21 to enclose the region of ionization including the cathode 12 and the anode 13. The shield 21 is supported on two posts 23 and, in turn, supports the disks 22. These posts, together with the'leads from the tube elements, are allJ sealed in a pinch 24 formed in the end seal of the tu e 11.

The conducting shield 21 and mica disks 22 also serve to prevent electrons from by-passing the control grid 14 and flowing to the anode support lead connection. Any degree of current tiow to the anode support will proportionally reduce the effectiveness of the grid control, since the by-passing current tlow would be entirely out of the field of iniiuence of the control grid. It the applied magnetic field is made strong enough, it will prevent the bypassing current leakage by its confining action on the straight line path of the normal electron low. However, the increase in magnetic flux density is greatly in excess of the amount required for grid control or for current increase. Therefore, the mica spacers 22 and shield 21 effectively reduce the amount of linx density required to prevent current leakage, and, in addition, both of them effectively reduce or prevent the accumulation of charges on the wall of the tube. It, under severe conditions, wall charges still accumulated suiciently to effect the tiow of current to the plate, the mica spacers 22 may be coated with a suitable conductive coating which is grounded to shield 21 or some other suitable point. The conductive coating covers substantially the entire area or each disk 22 but stops short of and is spaced from the grid, anode, and the cathode. AWhile the disks 22 have been indicated as being formed of mica, metal disks can be substituted for the, mica or used in conjunction with the nuca providing they were not used in such a manner as to short out the anode, grid, or cathode.

The use of the magnetic field in conjunction with the tube as hereinbefore described is believed to substantially reduce the amount of random motion of the electrons.

a tensity line of the electric field in such a manner that their paths are either straight or helical.

In the regions 16, which are the regions aligned with the grid wires 14, the accelerating potential is not large, andis, in addition, governed by the potential applied to the control grid 14. The electrons ionize the atoms of the gasv molecules and also recombine with the positive ions, thus forming a visual glow in the layers 16.

Near to the control grid 14, the positive ions which have been released are urged by the negative potential applied-to the grid to move toward it, surround it, and form a neutralizing positively charged sheath. However, the electrons constrained to these same layers i6, urged by their mutual repulsive charges, continue to fiow toward the grid 14 despite its repelling negative potential. They, thereforeZ tend to neutralize the positive ion sheath which would otherwise normally form around the grid wires, thus leaving the control grid free to repulse the electrons.

In the dark ionized regions 17, it is believed that the electrons are soenergized by the electric iield as to sele dom recombine with the ions they produce. This results in a strong ow of electrons toward the anode 13, and a lesser flow of positive ions toward the cathode 12, both contributing to the effective anode current.

It 1s believed that in the layers 17 of high electric intenslty alternating with the layers 16, the main portion of the space current flow to the plate is obtained. As the potential of the control grid 14 is driven more negative, the flow of electrons in the layers 16 is stopped just before the grid by its repelling potential. As the electrons are slowed down or stopped just before the grid, the reduction in speed of the electrons is suflicient to enable them easily to combine ,with the ions surrounding the grid wires. In addition, some of the ions that come close enough to the grid wires to touch them are also neutralized by removing electrons from the negatively charged wires. This can account for most of the current ow in the grid circuit which is higher than in a vacuum tube but still generally less than one percent of the plate current. Since the parallel magnetic field exerts a constraining action on the ions and electrons, the resultant channeling effect effectively reduces any tendency for random motion between stratified areas. Therefore, the amount of ions that can reach the grid wires in contrast to random motion, are thereby reduced enough in volume so that current output from the grid wires, plus the steady supply of low speed electrons in the sheath area, all combine to keep the grid wires sufficiently clear of ions to allow very eective grid action. Since the electrons and ions are held to fairly straight line movements, the grid wires also interpose a physical barrier in combination with the magnetic field to prevent any considerable number of electrons and ions from moving into a direct line between the grid wires and the anode. Consequently, there is always an area back of the grid wires, facing the anode, that is relatively free of both ions and electrons, equal to the cross-section diameter of the grid wires, due to grid barrier interference and to magnetic prevention of ions and electrons moving from adjacent channels into the ion-free region back of the grid wires.

When a negative potential is applied to the grid wires, the ion and electron-free region back of the grid wires gradually expands in area in proportion to the increase in grid voltage. This space charge-free gradually increases in size as the negative grid potential is increased and the electrons flowing between the space charge-free areas are gradually squeezed into increasingly narrow corridors between the grid wires. This reduced flow area also results in slowing down the speed of the electrons through the gradually narrowing region between the wires as they travel to the anode. Reducing the speed of the electrons at the grid region has several important effects. Due to the mutual repulsion effects of the electrons in the channels or regions 17, any flow restrictions at the grid region .also affect all of the electrons extending back to the cathode which are flowing in straight, chain link fashion, .toward the anode. Themain speed reduction seems to occur between the grid wires and the plate, crosswise of channels 17, and parallel to channels 17 between the grid wires and cathode at the outer edges of channels 17 immediately adjacent to channels 15. The speed reduction in channels 17, between the grid wires and the anode, seem to be due mainly to the lateral inuence of the backand sides of the grid wires. The lateral electron flow restriction in the grid-anode region causes a sudden reduction in speed in the grid-anode region, as characterized by a much higherrecombination of ions and electrons in this region, resulting in a much higher degree of visible light in this part of channel 17 than in a given area of channel 17 between the grid wires and the cathode. In addition, the lateral restriction at the grid wires causes a sufficient reduction in electron speed in channel 17 between the grid and cathode that enables the front portion of the grid wires to influence the outer electrons in channel 17, which are adjacent to channel 16, to further reduce their speed sufficiently for increased recombination effects to gradually widen chan* ne s 16.

The continual flow of electrons from the cathode causes layers 16 to expand laterally by the mutual repulsion of the negative charges and the reduction in electron velocity described. In consequence of this lateral ex` pansion of these layers 16, the layers 17 have less and less cross-section and so conduct less anode current. The magnitude of the .anode current is thus controlled by the expansion and contraction of the stratified ionized layers within the tube. This action is continued as the control grid 14 is driven increasingly more negative until the anode current has been reduced substantially to zero. These changes can be noted visually as an expansion of the visual layers 16 and in narrowing of the dark or clear layers 17.

The resistance effects of the grid on the anode current seem to be further proof of the grid control effects described and the extreme effectiveness of its control action. In tests with a high resistance in series with the anode, the tubed drop voltage (cathode to anode) was observed to rise gradually from l5 volts at full load conditions to several hundred volts when the grid had shut olf the anode current. When a low resistance is used in series with the anode, no such extreme change in tube drop will occur. Generally, only a few volts increase will be noted, unless the anode series resistance is almost zero and in that case no change in tube drop will be noted. As a further example of the extreme choking effect of the control grid and its extreme efiiciency, it will be noted that when a high resistance is in series (for example,

' 1000 to 4000 ohms) with the anode, the electron speed between the grid andthe anode will be less than when the grid is not exerting any influence and the tube drop is only 15 volts. This assumption is substantiated by the fact that when the tube drop is several hundred volts, the greatly increased glow in the grid anode region indicates that considerably more recombination takes place from slow electrons close to the anode than occurred when the tube drop was only l5 volts.

This high voltage, slow electron speed effect is quite important because it means that high anode voltages can be safely used through appropriate resistors and no destructive effects will occur on the anode area or cause cathode surface sputtering from high speed ions striking its surface. The grid prevents an excessive number of high speed electrons from hitting its surface and the increase in slow speed electrons for recombining with the ions moving toward the cathode prevents destructive cathode sputtering. f

The complete control of the grid extends up to and inclusive of any anode current sufficiently excessive of normal load requirements as to destroy the cathode. When the current load is sufficient to cause destructive effects on the cathode, the grid automatically becomes more effective and requires less grid voltage to control much more current. It has been found that if a minimum bias of 20% or 30% be maintained on the grid, the tube will automatically shut itself off before any harm is done, if the tube is suddenly shorted out.

The strength of the magnetic field necessary to effect stratification of the plasma is greater as the quantity of current flow is increased up to the extent necessary to control the mutual repulsion of the electrons and ions sufficiently to enable grid control. Field strengths between 50 and 1,500 gauss have been found suitable depending upon the magnitude of the current fiow. However, in general, the lower end of the field strengths will prove the most satisfactory, as surprisingly little magnetic flux density is required for grid control or to increase the current flow. Some flux densities too low to cause visible stratification have been successfully used and complete grid control was obtained.

A second embodiment of my invention is shown in Figure 3 of the drawing wherein an axial alignment of the tube elements and magnetic field are employed. More particularly, the tube 11 is made of glass or other suitable material and is gas-filled. A spiral filament 25 and a plate-like anode 26 are axially supported from opposite ends of the tube 11. In the space between the cathode 2S and the anode 26 of the control grid 27 is a second grid 28 which will herein be termed a screen grid. Surrounding the tube 11 is an annular solenoid 29 which when energized establishes an axially aligned field within the tube 11.

An electrostatic shield 30 encircles the ionization area to prevent accumulation of disruptive stray ion charges and to confine the ionization to a controlled region. A porcelain or lava ring 31 carried at the anode end of the shield 30 supports and laterally positions the grids 27 and 28 as well as the plate 26. The spacing between these elements 26, 27 and 28 is maintained by a pair of mica washers 32 of suitable thickness. A pinch 24 at the cathode end of the tube 11 supports and seals the leads from the tube'elements 16, 25, 27 and 28. A cap 33 at the opposite end of the tube 11 Supports and seals the lead 3 4 from the anode 26.

This tube operatesin substantially the sameA manner as that described in connection with the embodiment of the invention illustrated in Figures l and 2, but also has certain additional advantages' obtained as the result of the use of the additional grid 28. This screen grid 2 8 placed adjacent to the control grid 27 and on the cathode side thereof is preferably constructed of wires slightly larger in diameter than those of the control grid 27 and is aligned to shield the wires of the control grid 27 from cathode sputterings and from positive ions formed in the ionization layers.

In operation, the screen grid 2 8 should be held at a low positive potential. It will then attract electrons and repel positive ions. With fewer ions reaching the control grid 27 and more electrons available to combine with these positive ions, the likelihood of the formation of a positive ion sheath is further diminished. The effectiveness of the control grid 27, therefore, is made more stable and effective. ln addition, screen grid 28 serves several other highly useful functions. It provides a simple means of causing ionization almost up to the anode, even when the anode current is reduced to zero. In this manner, the normal ionization and cle-ionization time lag is reduced to a negligible factor, so much so that anode current frequencies in excess of one megacycle have been obtained, with no sign that the upper limit had been reached. Of course, practically the same frequency range can be obtained in the triode construction provided the anode current is not reduced to zero. If the anode current is reduced to zero, and the tube does not have a screen grid, the frequency characteristics will be reduced to that of a regular type thyratron. The screen grid also enables the control grid to have much more linear control over the anode current for the same voltage, than is obtainable from the triode type with the plate at the same distance from the cathode. Furthermore, the screen grid has an important effect on the internal tube drop between cathode and anode. It has been found in practice that the voltage drop between anode and cathode can be reduced to a surprising extent. ln some cases, peak anode current was obtained at anode voltages less than 6 volts. In the triode types, the anode voltages will generally run between l() to l volts. In all types of construction, the parallel magnetic iield helps reduce still further the anode voltage required for peak current.

The control and screen grids may be placed if desired in proximity to the cathode instead of the anode and exercise complete control over the anode current. However, for most purposes in a gas tube, the control and screen grids preferably should be placed close to the anode in order to be as far as possible way from the heat radiation from the cathode and to further reduce the possibility of the cathode sputtering material into the control grid. .It has been found also that grids adjacent both the cathode and anode may be used in combination, if desired, for special application.

It is also obvious that more than two grids can be used, if desired. Furthermore, any number of grids may be positive provided at least one grid is negative.

In Figure 4 of the drawing, a third embodiment of the present invention is illustrated wherein the tube elements are arranged in a manner suitable for push-pull action. The tube. as shown in Figure 4, has the appearance of a duo-triode. A eas-filled tube 11 encloses an indirectly heated cathode 12 located along the axis thereof. On diagonally opposite sides of the cathode 12 are located a pair of similar anodes 13. To control the space current flowing from the cathode 12 to these anodes 13, each anode is encircled by a control grid 14 which is, in turn, encircled by a screen grid 35. The wires of the screen grid 3S are preferably of larger diameter and laterally aligned with the wires of the control grid 14 so as to shield the latter from cathode sputterings and positive ions. This arrangement has been discussed in connection with Figure 3. It should be noted that the cathode sputterings are fragments of the high emission coating on the cathode which are often sputtered off during heavy load conditions and which will make the grid an emitter if they become lodged thereon.

.ln the tube of Figure 4. there is also provided a shielding cylinder 2i. of conducting material supported on posts 213i in tutu, Suppcrting insulating disks 22 on the shield ends to confine the discharge to a controlled region.

The posts und leads are all supported, and. .Sealed in a. pinch 24 formed in the tube 11'- Althuush a Common Cathode is employed, each plate 1,3 aud each Set 0f grids 14 and screen grids 35 act 'independently of one another to form a stratified plasma and in controlling the ionizing current formed therein. The two complete anode and grid structures are not only designed to allow push-pull operation off of one cathode, but, in addition, this type of construction has a very important function of providing a positive field of attraction for any electrons prevented from reaching the other anode. The resultant action permits much less grid voltage to be used to control the same amount of current to the anode than would be controlled in either Figure l or Figure 3. Even though the grid in either Figure l or Figure 3 will control a given amount of current at much less negative voltage than a vacuum tube could control the same amount of anode current, nevertheless the tube construction in Figure 4 will permit much more current to be controlled at much less voltage than that at which Figure l or Figure 3 can be operated.

It shouldV also be noted that the single magnetic field established by the pole faces 15 acts to cooperate with both electric fields in constraining the electron path.

From the foregoing description, it may be observed that neither the construction nor the operation of the invention is overly complex, the grid and the plate being of different potentials cooperate with the magnetic eld to stratify the plasma into alternate layers of high and low intensity. An abundant source of electrons is provided from the cathode, and upon these the magnetic field acts to constrain them from their normal random motion across the layer boundaries. In the low intensity layers, as represented by the iiow regions 16, the grid wires ata negative potential prevent the flow of electrons to the plate. The slot -moving electrons either fail to ionize the gas atoms or are easily recaptured by positive ions so that there is little space current flowing in these layers which I have designated as a low electric intensity region.

In the adjacent layers of high electric intensity, the swift moving electrons ionize the gas stronglybut are seldom recaptured by the ions. It is believed for this reason they pass onto the plate in increasing numbers, while the positive ions drift back to the cathode.

The major portion of the plate-to-cathode current is believed to flow in these dark regions of ionization between the grid wires where recombination seldom occurs. The continual control by the grid in the gas tube is obtained by the lateral expansion and contraction of the low intensity ionized regions 16, which encroach upon the high intensity layers, and thereby limit the space current carried by them. Were it not for the magnetic field, the negative grid wires would have been rendered ineffective by the formation of a positive ion sheath. The action of the magnetic field, however, constrains the electrons to flow toward the negatively charged grid where they will be recombined with the positive ions.

It has been further found that the flow lof current between the cathode and the plate may be controlled by maintaining the grid potential constant and by varying the strength of the magnetic eld. This method of control, however, has not been found to be as effective as maintaining a field of constant intensity and varying the charge on the control grid.

From the above description, it will be apparent that I have provided a gas-filled tube with the eiiicient operation of normal gas tubes but with the complete and continual control usually associated only with a Vacuum tube. Excepting for the narrow width of the cathode dark space, ionization extends from the cathode to the plate. This extensive ionization makes possible unusually high operating eiiiciencies. It will also be apparent that the construction is neither complex nor costly.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

l. In a gaseous conduction device including a sealed vessel containing an ionizable quantity of gas sufficient to support a gaseous discharge, a cathode heated to thermally emit electrons and an anode to establish an electric field, both enclosed in said vessel, a current control means comprising a control grid surrounding said anode and spaced therefrom a distance sufficient for gas ionization therebetween, and means for producing a magnetic field in substantial alignment with said electric field,

whereby a variable potential applied to said grid will control space current ow to said anode.

2. In a gaseous conduction device including a sealed vessel containing an ionizable quantity of gas sufiicient to support a gaseous discharge, a cathode heated to thermally emit electrons and an anode to establish an electric field, said anode and said cathode being enclosed in said vessel and spaced apart a distance greater than the mean free path of electrons in the gas, a space current control means comprising a control grid surrounding said anode,

a screen grid providing openings to said anode and substantially in alignment with openings in said control grid and surrounding said control grid, and means for producing a magnetic field in substantial alignment with said electric field, whereby a variable potential applied to said control grid will vary the space current ow to said anode and whereby said screen grid will physically and electrostatically shield said control grid from particles traveling toward said anode.

3. The combination comprising an electron discharge` device having a plate, a helically wound wire-type control grid surrounding said plate and in spaced relation thereto, and a cathode spaced a substantial distance from said control grid and said plate, and means establishing a magnetic field through said device and oriented substantially parallel to the general direction of iiow of space current in said device.

4. The combination comprising an electron discharge device having a plate, a helically wound wire-type control grid surrounding said plate and in spaced relation thereto, a helical wire screen grid surrounding said control grid, and a cathode spaced a substantial distance from said grids and said plate, the wire of said screen grid being in direct line between said control grid wire and said cathode, and means establishing a magnetic field through said device and oriented substantially parallel to the general direction of fiow of space current in said device.

5. The combination comprising an electron discharge device having a plate, a helically wound wire-type control grid surrounding said plate and in spaced relation thereto, a helical wire screen grid surrounding said control grid, and a cathode spaced a substantial distance from said grids and said plate, the wire of said screen grid being at least as large as the wire of said control grid and in direct line between said control grid wire and said cathode, antl means establishing a magnetic field through said device and oriented substantially parallel to the general direction of flow of space current in said device.

6. The combination comprising an electron discharge device having a plate, an electron-emitting element, a spirally-wound grid between said plate and said element, and means establishing a magnetic field through said device and oriented substantially parallel to the general direction of ow of space current in said device.

7. An electron discharge device comprising a gas-filled tube, a single cathode within said tube, a pair of anodes disposed respectively on opposite sides of said cathode, a pair of control grids disposed respectively between said anodes and said cathode, means exterior of said tube for establishing a magnetic field within said tube substantially parallel to the normal direction of electron flow between said cathode and said pair of anodes.

8. An electron discharge device comprising a gas-filled tube of generally tubular configuration, an electron-emitting cathode mounted centrally within said tube and substantially along the axis of said tube, a pair of anodes mounted on opposite sides respectively of said cathode extending substantially parallel thereto and within said tube, a plurality of grids within said tube between each of said anodes and said cathode, said grids having relatively wide openings therethrough, a conducting tubular shield within said tube and surrounding said anodes, said grids and said cathode, and a magnet mounted exteriorly of said tube and oriented to establish a magnetic field crosswise of said tube.

9. A gaseous conduction device comprising: a sealed y vessel containing an ionizable quantity of gas sufiicient to support a gaseous discharge, an electron-emitting cathode in said vessel, a first electrode in said vessel arranged to be at a positive potential relative to said cathode, a second electrode arranged to be at a negative potential relative to said first electrode and having a plurality of portions intermediate said first electrode and Said cathode and spaced from said first electrode a distance suificiently large for gas ionization therebetween, said portions being spaced from each other and from said electron-emitting cathode distances sufficiently large in relation to the spacing of said portions from said first electrode for acceleration of electrons to high velocities under the inuence of a positive potential on said first electrode and for little recombination of electrons and ions in first regions extending in between said portions, electron velocity being low and recombination of' electrons and ions being great in second regions aligned with said portions, and the relative size of said tirst and second regions and the current flow through the device being variable by varying the potential of said second electrode relative to said electron-emitting cathode.

l0. A gaseous conduction device comprising: a sealed vessel containing an ionizable quantity of gas sufficient to support a gaseous discharge, an electron-emitting cathode in said vessel, a first electrode in said Vessel arranged to be at a positive potential relative to said cathode, a second electrode arranged to be at a negative potential relative to said first electrode and having a plurality of portions intermediate said first electrode and said cathode and spaced from said first electrode a distance sufficiently large for gas ionization therebetween, said portions being spaced from each other and from said electron-emitting cathode distances sufficiently large in relation to the spacing of said portions from said first electrode for acceleration of electrons to high velocities under the influence of a positive potential on said first electrode and for little recombination of electrons and ions in first regions extending in between said portions, electron velocity being low and recombination of electrons and ions being great in second regions aligned with said portions, and means for inducing a magnetic field in the space between said cathode and said first electrode and aligned with the desired direction of electron movement in said first regions, the relative size of said first and second regions and the current flow through the device being variable by varying the potential of said second electrode relative to said electron-emitting cathode.

References Cited in the le of this patent UNITED STATES PATENTS 1,962,158 Smith .Tune 12, 1934 2,116,393 Griflith May 3, 1938 2,180,815 Meier Nov. 21, 1939 2,217,186 Smith Oct. 8, 1940 2,271,666 Smith Feb. 3, 1942 

